I had the perry performance group kit on my rxdi. It was a night and day difference, Proks, mpem reflash head and proks. I also put a prop on it and I work walk my buddy and we both had the same ski. It pissed him off so bad he ended up getting the kit.

1-jenny craig for about $300 you could lose as much as 20 pounds ..that's a deal of deals! Of course that mod has some unintended consequences in that you will have to mod your wardrobe a bit too.
2-Group K's site. If there is anything that can be done for a DI fuel map wise, that's where I'd be going. I recall reading something on that when I was really interested in the DI ( note-not anymore)

but in the end, the engine didn't have a whole lot of room, you're trading engine life for speed.

The 4-tec platform is a far better place to dump fat sacks of cash IMHO in exchange for speed. and these days the shortblocks for the two motors cost about the same

I'm really not sure because I don't try in RX di and I just can speak about my experience with engines.
If you have a computer you could advance the ignition timing. How much? depeding of fuel that you use in your country and if you can buy a "premium" fuel but in most of case you could advance 2-3 degrees even using "normal" fuel. As well us RX DI have knock sensor so if you have a maint light you could see and change set up.

For other hand you can modify propulsion... change impeller, change ride plate... but in most of case they need a "manual work" like repitch impeller, custom ride... not just buy and change